1. Field of the Invention
The present invention relates to an apparatus and method for increasing operation time in an IEEE802.15.4-2006 beacon based wireless sensor network (WSN), and more particularly to, an apparatus and method for increasing operation time with respect to the same amount of power consumption used by coordinators included in a WSN by reducing unnecessary standby power consumption required during an active period of a super frame.
2. Description of the Related Art
A wireless sensor network (WSN) uses a plurality of sensor nodes including a sensor that detects recognition information about an object or information about surroundings.
The WSN is a network system that connects to an external network in real time, processes information input through various sensors, and manages the information.
The WSN provides computing and communication functions, so as to realize a communication environment any time and anywhere irrespective of types of networks, devices, or services.
FIG. 1 illustrates a conventional IEEE802.15.4-2006 beacon based tree network that is a WSN system.
The IEEE802.15.4 standard concerns a physical layer and a data link layer of a lower rate wireless personal area network (WPAN).
The IEEE802.15.4 standard is a protocol that is directed toward a low rate communication bandwidth and low power, which is suitable for a device in a WPAN having a relatively short transmission distance and for realizing the WSN system.
The IEEE802.15.4-2006 standard has been revised to separate an active period of a super frame into a receiving region and a transmission region in order to prevent beacon collisions of coordinators, which is a problem of the IEEE802.15.4 standard.
Coordinators of an IEEE802.15.4-2006 beacon based WSN use a super frame structure to perform data communication.
Referring to FIG. 1, the super frame is managed by a PAN coordinator 100 and its range is determined according to a beacon frame transmitted by the PAN coordinator 100 every designated interval.
Each beacon frame includes network synchronization information of a plurality of network coordinators 110.
The network synchronization information includes a network address of a coordinator that is to receive data, a beacon order (BO) that determines a beacon interval (BI), and a super frame order (SO) that determines a super frame duration (SD) that is a super frame active period.
FIG. 2 illustrates a conventional super frame structure under the IEEE802.15.4-2006 standard. Referring to FIG. 2, the super frame structure includes two beacon frame periods 200 and 230, two active periods 210 and 240, and two non-active periods 220 and 250.
The beacon frame periods 200 and 230 include the beacon frame period 200 and the transmission beacon frame period 230.
The active periods 210 and 240 include the receiving super frame period 210 and the transmission super frame period 240 according to the receipt of a beacon and according to a transmission region.
The non-active periods 220 and 250 include the transmission period 220 and the receiving period 250.
Each coordinator uses the super frame structure to change a mode into a sleep mode during the non-active periods 220 and 250, thereby minimizing power consumption.
An SD and a BI are determined according to an SO value and a BO value, respectively. The SD and the BI are expressed according to equations 1 and 2 below,SD=basic SD*2SO symbols  (1)BI=basic SD*2BO symbols  (2)
wherein, the SO is greater than or equal to 0 and is smaller than or equal to the BO, and BO is greater than or equal to 0 and is smaller than or equal to 14.
If a minimum SD under the IEEE802.15.4 standard operating at 2.4 GHz is calculated by using equation 1, when SO=0, the minimum SD=15.36 msec.
Therefore, a coordinator following the conventional super frame structure under the IEEE802.15.4-2006 standard must maintain minimum transmission and receiving SDs and transmission and receiving super frame active periods 2*SD=30.72 msec when the coordinator does not receive data from an upper parent coordinator or a lower child coordinator.
The minimum transmission and receiving SDs increase when the SO value increases.
When the coordinator does not receive data from the upper parent coordinator or the lower child coordinator, the coordinator following the conventional super frame structure under the IEEE802.15.4-2006 standard is in a receiving standby state during the active periods, causing unnecessary standby power consumption.